Function render_config 

pub fn render_config(
    install_dir: &str,
    recipient: &str,
    s3: &S3Config,
    mirror: bool,
) -> String

Render the host’s config.toml: repos_root under install_dir, the age recipient (public key only — the private identity never leaves the client), and an [s3] table. endpoint is included only when the S3 config has one (real AWS S3 otherwise). mirror = true is appended only when mirror is set — the host’s backup arm gates the GitHub mirror on this line, so a non-mirror host omits it entirely rather than writing mirror = false.